<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link href="https://cdn.bootcdn.net/ajax/libs/twitter-bootstrap/3.1.0/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<form action="" method="post">
    <p>username: <input type="text" name="username">
    <span style="color: red;">{{ back_dic.username }}</span>
    </p>
    <p>
        password: <input type="text" name="password">
        <span style="color: red;">{{ back_dic.password }}</span>
    </p>

    <input type="submit" class="btn btn-success" value="提交">
</form>
</body>
</html>